In the field of ophthalmic cataract surgery, wherein a defect natural lens is replaced with an artificial lens, there has been a development towards lenses and methods, which inflict less surgical trauma. For many years most of the IOLs were made of poly(methylmethacrylate) (PMMA), a material with good optical characteristics and compatibility with tissues in the eye. A disadvantage of PMMA, however, is that it is a very rigid material and a surgical incision must be made large enough, at least 5–6 mm, for the implantation of the lens. With improved devices for removal of the natural lens by phacoemulsification, requiring only a rather small incision, there was a need for lenses with deformable optics, as disclosed in the U.S. Pat. No. 4,573,998 (Mazzocco). There are presently several types of foldable intraocular lenses on the market which can be inserted through a considerably smaller incision of about 3 to 4 mm, for example made from specifically designed silicone materials.
Even with the mentioned types of improved implantable IOLs, now available on the market, there is still a desire to obtain a lens which admits the use of an even smaller incision and behaves like the natural lens in the eye, i.e. will be accommodating with a focal point regulated by action of the ciliary muscle in the eye. In order to allow for a really small incision it would be necessary to form the lens inside the eye from a solution which is injected into the capsular bag or into a balloon placed inside the bag by means of a standard injection needle.
IOLs formed from an injected solution of a silicone prepolymer, crosslinker and catalyst have already been suggested in U.S. Pat. Nos. 5,278,258 and 5,391,590 (Gerace et al). Generally low temperature curing at body temperature means a slow process and up to 12 hours may be needed to complete their setting and their slow setting may result in material leakage out of the capsular bag through the surgical incision. In order to overcome this problem, U.S. Pat. Nos. 4,542,542 and 4,608,050 (Wright et al) disclose such a silicon based injected system which is partially cured by heat in the vicinity of the injection hole of the capsular bag to accomplish a first sealing effect.
Alternatively to thermocured silicone systems, photopolymerizable lens materials have been suggested which are activated after injection into the capsular by light in the presence of a photoinitiator. In the articles by Hettlich et al in German J Ophthalmol (1992), Vol. 1, pages 342–5 and 346–349, there are disclosures of how to employ photopolymerization of a monomer system injected into the capsular bag of the eye. An example of such an injectable system is also described in EP 414219, in which the liquid composition comprises a difunctional acrylate and/or methacrylate ester and a photoinitiator capable of being polymerized by light of a wavelength range between 400–500 nm. Further, the International patent application PCT/EP99/04715 is directed to an injectable photocurable aqueous solution of pre-polymerized units which is capable of forming a lens implant with a suitable elasticity modulus after final a crosslinking process triggered by visible light. Even if suitable polymerizable systems are at hand for preparing injectable lenses, there is still a considerable problem to obtain control of the refractive outcome of the eye after implantation. Accordingly, Hettlich et al suggested that by filling the capsular bag to varying degrees, or alternatively influencing the anterior or posterior capsular curvature, refractive control eventually would become possible.
O Nishi et al in Arch. Ophthalmol., 1997, Vol. 115, 507–510 describe experiments with direct injection of silicone material into the emptied capsular bag in cadaver pig eyes with subsequent plugging of the capsule and molding of the silicone into a synthetic lens. By using this procedure, the ability of the capsular bag to mold the injected silicone was investigated. It was found that different values of accommodation amplitude could be accomplished dependent on if the implanted lens was molded with a zonal tension applied on the capsule compared to when said tension was abolished. Nishi et al suggested that when (if) the eye is atropinized postoperatively, the lens capsule will conform to its non-accommodated state, which should yield the optimal amplitude of accommodation according to the investigated lens refilling principle. In the experiments referred to by H J Hettlich in Accommodative Lens Refilling Principles and Experiments© 1996 Pharmacia & Upjohn Groningen, the difficulties in obtaining the expected 30D myopic eye after lens injection are acknowledged.
Although there has been a considerable progress in the development of materials and surgical techniques for injectable lenses, considerable efforts are still needed to control the refractive outcome of this type of lenses. In particular, selection methods of suitable materials and improved control of the lens forming process after refilling the capsule will be necessary to carefully predict the refractive outcome of the eye subjected to lens replacement.